Study evaluates household transmission of COVID-19
Among household contacts of patients who were diagnosed with COVID-19, approximately one-tenth subsequently tested positive for the novel coronavirus, according to research published in JAMA Network Open.
“Using the electronic medical record system of a large integrated health system, we were able to measure the risk of household transmission of COVID-19 during the first half of the pandemic,” Joshua P. Metlay, MD, PhD, chief of the division of general internal medicine at Massachusetts General Hospital, told Healio Primary Care. “The risk of transmission from an infected index case to a household member was 10% during the study period, which emphasizes the need for prevention measures within households of patients with COVID-19, especially for higher risk patients.”
Metlay and colleagues conducted a retrospective cohort study to assess the risk for COVID-19 infection among household contacts. The index COVID-19 cases in the study were diagnosed from March 4, 2020, through May 17, 2020, in the Mass General Brigham health system.
The researchers identified index cases based on positive reverse transcriptase-polymerase chain reaction test results, and identified the at-risk cohort by finding all patients registered at the same address as the index case, excluding those who had not visited the health system at least once in the last 60 months. They used electronic health records to collect information on the characteristics of household contacts of index cases.
A total of 7,262 index cases with 17,917 at-risk individuals linked to the same addresses were included in the study.
Among at-risk individuals, 52.1% were female, and 38.4% lived in households with six to 10 people.
Metlay and colleagues found an overall incidence of 10.1% among those at risk for COVID-19 exposure through a household contact.
They determined that, after the index case, the median time to diagnosis in at-risk individuals who were later diagnosed with COVID-19 was 3 days (IRQ = 1-9 days).
Additionally, they found that independent factors associated with an increased transmission risk included those aged older than 18 years and with multiple comorbid conditions.
According to results from sensitivity analyses that limited the maximum household size to two people, the transmission risk increased to 13.8%.
“Best practice for reducing household transmission remains an area of significant uncertainty,” Metlay said. “However, based on data from hospital settings, we believe that social distancing, hand hygiene and mask wearing all contribute to risk reduction during the 10 day window of presumed infectivity after diagnosis.”